Manufacturing method of positive active material precursor for sodium rechargeable batteries, positive active material precursor for sodium rechargeable batteries made by the same, and manufacturing method of positive active material for sodium rechargeable batteries, positive active material for sodium rechargeable batteries made by the same

ABSTRACT

Disclosed is a method for producing a cathode active material precursor for a sodium secondary battery by using a coprecipitation technique and a cathode active material precursor for a sodium secondary battery produced thereby, and a cathode active material for a sodium secondary battery using the cathode active material precursor for a sodium secondary battery and a method for producing the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of PCT/KR2013/010520 filedNov. 19, 2013 and PCT/KR2013/010521 filed Nov. 19, 2013, both of whichclaim the benefit of Korean patent applications KR 10-2012-0130824 filedNov. 19, 2012, KR 10-2013-0140907 filed Nov. 19, 2013, KR10-2012-0131027 filed Nov. 19, 2012, and KR 10-2013-0140911 filed Nov.19, 2013, the contents of each of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

Embodiments of the inventive concepts described herein relate to amethod for producing a cathode active material precursor for a sodiumsecondary battery by using a coprecipitation technique and a cathodeactive material precursor for a sodium secondary battery producedthereby, and a cathode active material for a sodium secondary batteryusing the cathode active material precursor for a sodium secondarybattery and a method for producing the same.

BACKGROUND OF THE INVENTION

At present, a lithium ion secondary battery using a non-aqueouselectrolytic solution prepared by dissolving an electrolytic salt in anon-aqueous solvent and a lithium ion moving between the anode and thecathode for charging and discharging is widely used as a secondarybattery having a high energy density. A lithium ion battery whichcontains a lithium transition metal oxide as the cathode material andutilizes a lithium ion insertion reaction is commercially available.However, lithium contained in the lithium ion battery is expensive, andthus a battery which is inexpensive and has a higher capacity isrequired.

Recently, research on a sodium ion secondary battery using a sodium ioninstead of a lithium ion has been started. It is possible to produce asecondary battery at low cost if a secondary battery using a sodium ioninstead of a lithium ion is successfully produced since sodium is anabundant resource having a great amount of deposits.

In JP 2007-287661 A, a secondary battery including a positive electrodeusing a composite metal oxide obtained by calcining a raw materialhaving a composition ratio (Na:Mn:Co) of Na, Mn and Co of 0.7:0.5:0.5and a negative electrode composed of a sodium metal is specificallydescribed. In addition, in JP 2005-317511 A, α-NaFeO₂ having a hexagonal(layered rock salt-type) crystal structure is specifically disclosed asa composite metal oxide and this composite metal oxide is obtained bymixing Na₂O₂ and Fe₃O₄ and calcining the mixture at from 600 to 700° C.in the air. However, a sodium secondary battery of the prior art is notsatisfactory in lifespan characteristics, that is, the dischargecapacity retention when the charge and discharge is repeated.

The most general method to produce a cathode active material for alithium secondary battery or a sodium secondary battery of the prior artis a solid phase reaction method in which the powders of carbonate saltsor hydroxides of the respective constituent elements as raw materialsare subjected to the mixing and calcining process several times.However, the solid phase reaction method has disadvantages that it isdifficult to form the solid solutions of the solid phases, impuritiesare easily mixed therein at the time of mixing, it is difficult touniformly control the size of particles, and a high temperature and along production time are required at the time of manufacture.

On the other hand, among the wet methods, the coprecipitation techniquehas advantages that it is possible to control the constituent elementsin the atomic range and to produce a spherical composite metalcarbonate. However, the solid phase reaction method is mainly adopted inorder to produce a cathode active material for a sodium secondarybattery of the prior art, but the method to produce a cathode activematerial precursor and a cathode active material for a sodium secondarybattery by adopting the coprecipitation technique is rarelyinvestigated.

SUMMARY OF THE INVENTION Problems to Solve

Embodiments of the inventive concepts provide a method for producing acathode active material precursor for a sodium secondary battery byusing a coprecipitation technique and a cathode active materialprecursor for a sodium secondary battery produced thereby.

Embodiments of the inventive concepts also provide a cathode activematerial for a sodium secondary battery using the cathode activematerial precursor for a sodium secondary battery and a method forproducing the same.

Tools for Problem Solving

One aspect of embodiments of the inventive concept is directed toprovide a method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique, themethod including:

(a) introducing distilled water and a first pH adjusting agent into acoprecipitation reactor, supplying air or a nitrogen gas to the reactor,and maintaining a pH in the reactor at from 6.5 to 7.5 while stirring;

(b) adjusting the pH in the reactor at from 6.5 to 11 by continuouslyintroducing a second pH adjusting agent into the and mixing the mixture;and

(c) forming particles of a cathode active material precursor for asodium secondary battery by introducing an aqueous solution oftransition metal compounds containing a nickel salt, an iron salt, and amanganese salt in an equivalent ratio and a complexing agent into thereactor.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique, ammoniaor ammonium sulfate may be used as the first pH adjusting agent.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept, the second pH adjustingagent in (b) above is ammonium oxalate, KOH, or NaOH.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept, the pH in the reactor isadjusted to from 10 to 11 in the case of introducing NaOH or KOH as thesecond pH adjusting agent in (b) above and the pH in the reactor isadjusted to from 6.5 to 11 in the case of introducing ammonium oxalateas the second pH adjusting agent in (b) above.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept, the nickel salt is selectedfrom the group consisting of nickel sulfate, nickel nitrate, nickelchloride, nickel fluoride, nickel acetate, and nickel hydroxide, theiron salt is selected from the group consisting of iron sulfate, ironnitrate, iron chloride, iron fluoride, iron acetate, and iron hydroxide,and the manganese salt is selected from the group consisting ofmanganese sulfate, manganese nitrate, manganese chloride, manganesefluoride, manganese acetate, and manganese hydroxide in (c) above.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept, the complexing agent isselected from the group consisting of an aqueous solution of ammonia(NH₄OH), ammonium sulfate ((NH₄)₂SO₄), ammonium nitrate (NH₄NO₃), anddiammonium hydrogen phosphate ((NH₄)₂HPO₄) in (c) above.

In the method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept, a ratio of a concentrationof the complexing agent to a concentration of the aqueous solution of atransition metal compound is from 0.8 to 1.2 in (c) above.

Another aspect of embodiments of the inventive concept is directed toprovide a cathode active material precursor for a sodium secondarybattery, which is produced by the method for producing a cathode activematerial precursor according to the embodiments of the inventiveconcept, has a spherical shape having a particle size of from 5 to 15μm, and exhibits a monodisperse type particle size distribution.

The cathode active material precursor for a sodium secondary batteryaccording to the embodiments of the inventive concept is represented byany one of the following Chemical Formulas 1 to 3:

Ni_(x)Fe_(y)Mn_(1-x-y)(OH)₂ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5);  [Chemical Formula 1]

Ni_(x)Fe_(y)Mn_(1-x-y)C₂O₄ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5);  [Chemical Formula 2]

and

[Ni_(x)Fe_(y)Mn_(1-x-y)]₃O₄ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5).  [Chemical Formula 3]

Still another aspect of embodiments of the inventive concept is directedto provide a cathode active material for a sodium secondary batteryproduced using the cathode active material precursor for a sodiumsecondary battery according to the embodiments of the inventive concept.

The cathode active material for a sodium secondary battery according tothe embodiments of the inventive concept is represented byNa_(x)[Ni_(y)Fe_(z)Mn_(1-y-z)]O₂ (0.8≦x≦1.2, 0.05≦y≦0.9, 0.05≦z≦0.9,0.05≦1-y-z≦0.9) and has an O₃-type crystal structure.

The cathode active material for a sodium secondary battery according tothe embodiments of the inventive concept has a spherical shape having aparticle size of from 5 to 15 μm and exhibits a monodisperse typeparticle size distribution.

The cathode active material for a sodium secondary battery according tothe embodiments of the inventive concept has three peaks appearing at2θ=in a range of from 30° to 40° and the peak (104) of a main peakappearing at 2θ=in a range of from 40° to 45° in XRD pattern.

The cathode active material for a sodium secondary battery according tothe embodiments of the inventive concept has a tapped density of from1.0 to 2.4 g/cc.

Yet another aspect of embodiments of the inventive concept is directedto provide a method for producing a cathode active material for a sodiumsecondary battery according to the embodiments of the inventive concept,the method including:

mixing the cathode active material precursor for a sodium secondarybattery according to the embodiments of the inventive concept; and

subjecting the mixture thus obtained to a heat treatment.

In the method for producing a cathode active material for a sodiumsecondary battery according to the embodiments of the inventive concept,the sodium compound is sodium carbonate, sodium nitrate, sodium acetate,sodium hydroxide, hydrates of sodium hydroxide, sodium oxide, or one oftheir combinations.

In the method for producing a cathode active material for a sodiumsecondary battery according to the embodiments of the inventive concept,the heat treatment is conducted at from 800° C. to 1000° C.

Still yet another aspect of embodiments of the inventive concept isdirected to provide a sodium secondary battery including the cathodeactive material for a sodium secondary battery according to theembodiments of the inventive concept.

Effect of the Invention

The method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto the embodiments of the inventive concept utilizes a coprecipitationtechnique and appropriately adjusts the kind of the complexing agent andthe pH value so that a cathode active material precursor for a sodiumsecondary battery which exhibits improved lifespan characteristics andhas a new composition and a cathode active material for a sodiumsecondary battery using this precursor can be provided.

BRIEF DESCRIPTION OF THE FIGURES

The above and other objects and features will become apparent from thefollowing description with reference to the following figures, whereinlike reference numerals refer to like parts throughout the variousfigures unless otherwise specified, and wherein

FIGS. 1 to 4 illustrate the SEM images of the precursors produced inExamples of the embodiments of the inventive concept.

FIGS. 5 to 8 illustrate the measurement results of the particle sizedistribution of the precursors produced in Examples of the embodimentsof the inventive concept.

FIGS. 9 and 10 illustrate the measurement results of XRD of theprecursors produced in Examples of the embodiments of the inventiveconcept.

FIG. 11 illustrates the measurement results of the particle sizedistribution of the precursors produced in Examples of the embodimentsof the inventive concept.

FIGS. 12 and 13 illustrate the SEM images of the precursors produced inExamples of the embodiments of the inventive concept.

FIGS. 14 and 15 illustrate the measurement results of the particle sizedistribution of the precursors produced in Examples of the embodimentsof the inventive concept.

FIGS. 16 to 23 illustrate the measurement results of XRD of the cathodeactive material produced in an Example of the embodiments of theinventive concept.

FIGS. 24 and 25 illustrate the SEM images of the cathode active materialproduced in an Example of the embodiments of the inventive concept.

FIGS. 26 to 36 illustrate the measurement results of the charge anddischarge characteristics and lifespan characteristics of a batterycontaining the cathode active material produced in an Example of theembodiments of the inventive concept.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the embodiments of the inventive concept will be explainedin more detail with reference to Examples, but the embodiments of theinventive concept are not limited thereto.

Examples 1 to 4

In a reactor, 4 L of distilled water filled and stirred at 1000 rpmwhile adding ammonia as the first pH adjusting agent so as to maintainthe pH in the reactor at 7 and the internal temperature at 50° C. Intothe reactor, a 4 M NaOH solution as the second pH adjusting agent wasintroduced and the pH in the reactor was adjusted to 10.2 and maintainedfor 30 minutes.

As an aqueous solution of transition metal compounds, NiSO₄.6H₂O,FeSO₄.7H₂O, and MnSO₄.5H₂O were mixed together in an equivalent ratioand introduced into the reactor together with NH₄OH as the complexingagent, thereby producing a precursor represented byNi_(0.25)Fe_(0.25)Mn_(0.5)(OH)₂ as presented in the following Table 1.

The precursors of Examples 2 to 4 respectively represented byNi_(0.25)Fe_(0.35)Mn_(0.4)(OH)₂, Ni_(0.25)Fe_(0.5)Mn_(0.25)(OH)₂ andNi_(0.15)Fe_(0.35)Mn_(0.5)(OH)₂ were produced in the same manner as inExample 1 except that the mixing ratio of the aqueous solution oftransition metal compounds was adjusted in Example 1.

TABLE 1 Division Composition Example 1 Ni_(0.25)Fe_(0.25)Mn_(0.5)(OH)₂Example 2 Ni_(0.25)Fe_(0.35)Mn_(0.4)(OH)₂ Example 3Ni_(0.25)Fe_(0.5)Mn_(0.25)(OH)₂ Example 4Ni_(0.15)Fe_(0.35)Mn_(0.5)(OH)₂ Example 5 Ni_(0.25)Fe_(0.5)Mn_(0.25)C₂O₄Example 6 Ni_(0.2)Fe_(0.6)Mn_(0.2)C₂O₄ Example 7Ni_(0.17)Fe_(0.66)Mn_(0.17)C₂O₄ Example 8 Ni_(0.2)Fe_(0.55)Mn_(0.25)C₂O₄Example 9 Ni_(0.3)Fe_(0.45)Mn_(0.25)C₂O₄ Example 10Ni_(0.35)Fe_(0.4)Mn_(0.25)C₂O₄ Example 11 Ni_(0.4)Fe_(0.35)Mn_(0.25)C₂O₄Example 12 Ni_(0.45)Fe_(0.3)Mn_(0.25)C₂O₄ Example 13(Ni_(0.25)Fe_(0.5)Mn_(0.25))₃O₄ Example 14(Ni_(0.25)Fe_(0.25)Mn_(0.5))₃O₄

Experimental Example 1 Taking of SEM Image

The SEM images of the precursors produced in Examples 1 to 4 were takenand the images taken are illustrated in FIGS. 1 to 4.

Experimental Example 2 Measurement of particle size distribution

The particle size distribution of the precursors produced in Examples 1to 4 was measured and the results are illustrated in FIGS. 5 to 8.

It can be seen that the particle size distribution of the precursorparticles produced in Examples of the embodiments of the inventiveconcept is a monodisperse type from FIGS. 5 to 8.

Examples 5 to 12

The precursors of Examples 5 to 12 were produced in the same manner asin Example 1 except that the pH in the reactor was adjusted to 7 usingammonia as the first pH adjusting agent, the pH in the reactor wasadjusted to 7 using a 0.5 M aqueous solution of ammonium oxalate as thesecond pH adjusting agent and the mixing ratio of the aqueous solutionof transition metal compounds was adjusted so as to have thecompositions as presented in Table 1 above.

Experimental Example 3 Measurement of XRD

The precursors produced in Examples 5 to 7 were subjected to the XRDmeasurement and the results are illustrated in FIG. 9.

The precursors produced in Examples 5 and 8 to 12 were subjected to theXRD measurement and the results are illustrated in FIG. 10.

Experimental Example 4 Measurement of particle size distribution

The particle size distribution of the precursor produced in Example 5was measured and the results are illustrated in FIG. 11.

Examples 13 and 14

The precursors of Examples 13 and 14 were produced in the same manner asin Example 1 except that the pH in the reactor was adjusted to 7 usingammonia as the first pH adjusting agent, the pH in the reactor wasadjusted to 9.2 adding a 4 M NaOH solution as the second pH adjustingagent, and the mixing ratio of the aqueous solution of transition metalcompounds was adjusted so as to have the compositions as presented inTable 1 above.

Experimental Example 5 Taking of SEM Image

The SEM images of the precursors produced in Examples 13 and 14 weretaken and the images taken are illustrated in FIGS. 12 and 13.

Experimental Example 6 Measurement of Particle Size Distribution

The particle size distribution of the precursors produced in Examples 8and 9 was measured and the results are illustrated in FIGS. 14 and 15.It can be seen that the particle size distribution of the precursorsproduced in Examples of the embodiments of the inventive concept is amonodisperse type from FIGS. 14 and 15.

Examples Production of Cathode Active Material

The cathode active materials of Examples 15 to 28 were produced bymixing and stirring sodium carbonate as the sodium compound with theprecursors produced in Examples 1 to 14 above and then subjecting themixture thus obtained to a heat treatment.

Experimental Example Measurement of XRD

The measurement results of XRD of the cathode active materials producedin Examples 15 to 18 are illustrated in FIGS. 16 to 19, respectively,the measurement results of XRD of the cathode active materials producedin Examples 17 to 19 are illustrated in FIG. 20, the measurement resultsof XRD of the cathode active materials produced in Examples 20 to 22 areillustrated in FIG. 21, and FIG. 20, and the measurement results of XRDof the cathode active materials produced in Examples 23 and 24 areillustrated in FIGS. 22 and 23.

It can be seen that three peaks appear at 2θ=in a range of from 30° to40° and the (104) main peak that is a characteristic of an O₃-typecrystal structure appears at 2θ=in a range of from 40° to 45° in XRDpattern of the cathode active materials for a sodium secondary batteryproduced in Examples of the embodiments of the inventive concept.

Experimental Example Taking of SEM Image

The SEM images of the cathode active material that was produced inExample 19 and represented by [Ni_(0.25)Fe_(0.5)Mn_(0.25)]O₂ and thecathode active material that was produced in Example 28 and representedby [Ni_(0.25)Fe_(0.25)Mn_(0.5)]O₂ were taken and the images taken areillustrated in FIGS. 24 and 25.

Production Example Production of Battery

The composite metal oxide E1, acetylene black (manufactured by DENKIKAGAKU KOGYO KABUSHIKI KAISHA) as the electrically conductive material,and PVDF (PolyVinylideneDiFluoridePolyflon manufactured by KUREHACORPORATION) as the binder were respectively weighed so as to have acomposition of composite metal oxide:electrically conductivematerial:binder=85:10:5 (weight ratio).

Thereafter, first the composite metal oxide and acetylene black werethoroughly mixed using an agate mortar, N-methyl-2-pyrrolidone (NMP,manufactured by Tokyo chemical industry Co., Ltd.) was added to thismixture in an appropriate amount, PVDF was then further added thereto,and the resultant was uniformly mixed to obtain a slurry. The slurrythus obtained was coated on an aluminum foil having a thickness of 40 μmas the current collector using an applicator so as to have a thicknessof 100 this was then placed in a dryer and thoroughly dried whileremoving NMP, thereby obtaining a cathode sheet. This cathode sheet waspunched using an electrode punching machine so as to have a diameter of1.5 cm and then sufficiently pressed using a hand press, therebyfabricating a cathode.

The cathode thus fabricated was placed in the recess of the lower partof a coin cell (manufactured by Hohsen Corporation) such that thealuminum foil faces down, subsequently 1 M NaClO₄/propylene carbonate+2vol % fluoroethylene carbonate (FEC) as the non-aqueous electrolyticsolution, a polypropylene porous film (thickness: 20 μm) as theseparator, and a sodium metal as the anode were then combined therewith,thereby fabricating a sodium secondary battery.

Experimental Example Measurement of Charge and Discharge Characteristics

The measurement results of the charge and discharge characteristics ofthe sodium secondary batteries containing the active materials ofExamples 15 to 21 and Example 27 produced from the precursors ofExamples 1 to 7 and Examples 13 are presented in the following Table 2.

From the following Table 2, it can be seen that the batteries containingthe active materials produced using the cathode active materialprecursors for a sodium secondary battery produced by the embodiments ofthe inventive concept exhibit an initial charge and discharge efficiencyof 90% or more.

TABLE 2 Sintering conditions and charge 1^(st) Division and dischargeconditions 0.2 C 1^(st) Efficiency Example 1Ni_(0.25)Fe_(0.25)Mn_(0.5)(OH)₂ precursor 155.5 mAh/g 94.1% Example Na95%, 970° C./24 h sintered, 15 4.3 V Example 2Ni_(0.25)Fe_(0.35)Mn_(0.4)(OH)₂ precursor 180.1 mAh/g 101.2%  Example Na98%, 900° C./24 h sintered, 16 4.3 V Ni_(0.25)Fe_(0.35)Mn_(0.4)(OH)₂precursor 176.3 mAh/g 100.9%  Na 98%, 930° C./24 h sintered, 4.3 VNi_(0.25)Fe_(0.35)Mn_(0.4)(OH)2 precursor 166.2 mAh/g 95.4% Na 98%, 970°C./24 h sintered, 4.3 V Example 3 Ni_(0.25)Fe_(0.5)Mn_(0.25)(OH)₂precursor 130.7 mAh/g 91.6% Example Na 98%, 970° C./24 h sintered, 173.9 V Example 4 Ni_(0.15)Fe_(0.35)Mn_(0.5)(OH)₂ precursor 141.3 mAh/g 104% Example Na 98%, 970° C./24 h sintered, 18 4.3 V Example 5Ni_(0.25)Fe_(0.5)Mn_(0.25)C₂O₄ precursor 135.7 mAh/g 93.4% Example Na98%, 950° C./24 h sintered, 19 3.9 V Example 6Ni_(0.2)Fe_(0.6)Mn_(0.2)C₂O₄ precursor 123.0 mAh/g 93.6% Example Na 98%,950° C./24 h sintered, 20 3.8 V Example 7Ni_(0.17)Fe_(0.66)Mn_(0.17)C₂O₄, precursor 116.8 mAh/g 91.8% Example Na98%, 950° C./24 h sintered, 21 3.7 V Example(Ni_(0.25)Fe_(0.5)Mn_(0.25))₃O₄ precursor 124.3 mAh/g 92.1% 13 Na 98%,970° C./24 h sintered, Example 3.9 V 27

Experimental Example Measurement of Lifespan Characteristics

The measurement results of the charge and discharge characteristics ofthe sodium secondary batteries containing the active materials ofExamples 15 to 18 and Example 22 produced from the precursors producedin Examples 1 to 4 and Example 8 are presented in the following Table 3.

The measurement results of the charge and discharge characteristics ofthe sodium secondary batteries containing the active materials producedfrom the precursors produced in Examples 1 to 4 are illustrated in FIGS.26 to 29, the measurement results of the charge and dischargecharacteristics and lifespan characteristics of the sodium secondarybatteries containing the active materials produced from the precursorsproduced in Examples 5 to 7 are illustrated in FIGS. 30 and 31, themeasurement results of the charge and discharge characteristics andlifespan characteristics of the sodium secondary batteries containingthe active materials produced from the precursors produced in Example 5and Examples 8 to 10 are illustrated in FIGS. 32 to 34, and themeasurement results of the charge and discharge characteristics andlifespan characteristics of the sodium secondary batteries containingthe active materials which have been produced from the precursorsproduced in Examples 11 and 12 and have an O₃-type crystal structure areillustrated in FIGS. 35 and 36.

TABLE 3 0.2 C 0.5 C 0.5 C Division 0.2 C 1^(st) 0.2 C 20^(th) retention0.5 C 1^(st) 20^(th) retention Example 1 155.5 mAh/g 130.2 mAh/g 83.7%106.9 mAh/g  96.0 mAh/g 89.8% Example 15 Example 2 180.1 mAh/g 141.3mAh/g 78.5% 125.6 mAh/g 117.5 mAh/g 93.6% Example 16 176.3 mAh/g 140.5mAh/g 76.7% 125.9 mAh/g 117.8 mAh/g 93.6% 166.2 mAh/g 124.6 mAh/g 75.0%107.7 mAh/g  95.1 mAh/g 88.3% Example 3 130.7 mAh/g 122.0 mAh/g 93.3%114.3 mAh/g 105.4 mAh/g 92.2% Example 17 Example 4 141.3 mAh/g 119.9mAh/g 84.9%  90.7 mAh/g  81.7 mAh/g 90.1% Example 18 Example 8 124.3mAh/g 114.7 mAh/g 92.3% 106.5 mAh/g 100.7 mAh/g 94.6% Example 22

From Table 3, it can be seen that the sodium secondary batteriescontaining the precursors produced by the embodiments of the inventiveconcept have a charge and discharge efficiency of about 90% until the20th cycle to exhibit significantly excellent lifespan characteristics.

While the inventive concept has been described with reference toexemplary embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the inventive concept. Therefore, it shouldbe understood that the above embodiments are not limiting, butillustrative.

What is claimed is:
 1. A method for producing a cathode active materialprecursor for a sodium secondary battery by using a coprecipitationtechnique, the method comprising: (a) introducing distilled water and afirst pH adjusting agent into a coprecipitation reactor, supplying airor a nitrogen gas to the reactor, and maintaining a pH in the reactor atfrom 6.5 to 7.5 while stirring; (b) adjusting the pH in the reactor atfrom 6.5 to 11 by continuously introducing a second pH adjusting agentinto the reactor and mixing the mixture; and (c) forming particles of acathode active material precursor for a sodium secondary battery byintroducing an aqueous solution of transition metal compounds containinga nickel salt, an iron salt, and a manganese salt in an equivalent ratioand a complexing agent into the reactor.
 2. The method for producing acathode active material precursor for a sodium secondary battery byusing a coprecipitation technique according to claim 1, wherein thefirst pH adjusting agent in (a) above is ammonia or ammonium sulfate. 3.The method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto claim 1, wherein the second pH adjusting agent in (b) above isselected from the group consisting of ammonium oxalate, KOH, and NaOH.4. The method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto claim 3, wherein the pH in the reactor is adjusted to from 10 to 11in the case of introducing NaOH or KOH as the second pH adjusting agentin (b) above.
 5. The method for producing a cathode active materialprecursor for a sodium secondary battery by using a coprecipitationtechnique according to claim 3, wherein the pH in the reactor isadjusted to from 6.5 to 11 in the case of introducing ammonium oxalateas the second pH adjusting agent in (b) above.
 6. The method forproducing a cathode active material precursor for a sodium secondarybattery by using a coprecipitation technique according to claim 1,wherein the nickel salt is selected from the group consisting of nickelsulfate, nickel nitrate, nickel chloride, nickel fluoride, nickelacetate, and nickel hydroxide, the iron salt is selected from the groupconsisting of iron sulfate, iron nitrate, iron chloride, iron fluoride,iron acetate, and iron hydroxide, and the manganese salt is selectedfrom the group consisting of manganese sulfate, manganese nitrate,manganese chloride, manganese fluoride, manganese acetate, and manganesehydroxide in (c) above.
 7. The method for producing a cathode activematerial precursor for a sodium secondary battery by using acoprecipitation technique according to claim 1, wherein the complexingagent is selected from the group consisting of an aqueous solution ofammonia (NH₄OH), ammonium sulfate ((NH₄)₂SO₄), ammonium nitrate(NH₄NO₃), and diammonium hydrogen phosphate ((NH₄)₂HPO₄) in (c) above.8. The method for producing a cathode active material precursor for asodium secondary battery by using a coprecipitation technique accordingto claim 1, wherein a ratio of a concentration of the complexing agentto a concentration of the aqueous solution of transition metal compoundsis from 0.8 to 1.2 in (c) above.
 9. A cathode active material precursorfor a sodium secondary battery has a spherical shape having a particlesize of from 5 to 15 μm, and exhibits a monodisperse type particle sizedistribution.
 10. The cathode active material precursor for a sodiumsecondary battery according to claim 9, which is represented by any oneof the following Chemical Formulas 1 to 3:Ni_(x)Fe_(y)Mn_(1-x-y)(OH)₂ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5);  [Chemical Formula 1]Ni_(x)Fe_(y)Mn_(1-x-y)C₂O₄ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5);  [Chemical Formula 2]and[Ni_(x)Fe_(y)Mn_(1-x-y)]₃O₄ (0.1≦x≦0.3, 0.2≦y≦0.7,0.1≦1-x-y≦0.5).  [Chemical Formula 3]
 11. A cathode active material fora sodium secondary battery produced using the cathode active materialprecursor for a sodium secondary battery according to claim
 9. 12. Thecathode active material for a sodium secondary battery according toclaim 11, which is represented by Na_(x)[Ni_(y)Fe_(z)Mn_(1-y-z)]O₂(0.8≦x≦1.2, 0.05≦y≦0.9, 0.05≦z≦0.9, 0.05≦1-y-z≦0.9) and has an O₃-typecrystal structure.
 13. The cathode active material for a sodiumsecondary battery according to claim 11, which has a spherical shapehaving a particle size of from 5 to 15 μm and exhibits a monodispersetype particle size distribution.
 14. The cathode active material for asodium secondary battery according to claim 11, which has three peaksappearing at 2θ=in a range of from 30° to 40° and the peak (104) of amain peak appearing at 2θ=in a range of from 40° to 45° in XRD pattern.15. The cathode active material for a sodium secondary battery accordingto claim 11, which has a tapped density of from 1.0 to 2.4 g/cc.
 16. Amethod for producing the cathode active material for a sodium secondarybattery, the method comprising: mixing the cathode active materialprecursor for a sodium secondary battery according to claim 9 and asodium compound; and subjecting the mixture thus obtained to a heattreatment.
 17. The method for producing a cathode active material for asodium secondary battery according to claim 16, wherein the sodiumcompound is sodium carbonate, sodium nitrate, sodium acetate, sodiumhydroxide, hydrates of sodium hydroxide, sodium oxide, or one of theircombinations.
 18. The method for producing a cathode active material fora sodium secondary battery according to claim 16, wherein the sodiumcompound is mixed in a ratio of from 1.0 to 1.5 mole per 1 mole of thecathode active material precursor for a sodium secondary battery. 19.The method for producing a cathode active material for a sodiumsecondary battery according to claim 16, wherein the heat treatment isconducted at from 800° C. to 1000° C.
 20. A sodium secondary batterycomprising the cathode active material for a sodium secondary batteryaccording to claim 15.